export default function initLoginBg(){
    var windowWidth = document.documentElement.clientWidth || document.body.clientWidth;
  var windowHeight = document.documentElement.clientHeight || document.body.clientHeight;
  // var windowWidth = window.clientWidth;
  // var windowHeight = window.clientHeight;
  var canvas = document.getElementById('canvas') as HTMLCanvasElement,
  ctx = canvas.getContext('2d') as CanvasRenderingContext2D,
  w = canvas.width = windowWidth,
  h = canvas.height = windowHeight,
  
  hue = 217,
  stars:IntStart[] = [],
  count = 0,
  maxStars = 400;//星星数量
  
  var canvas2 = document.createElement('canvas') ,
  ctx2 = canvas2.getContext('2d') as CanvasRenderingContext2D;
  canvas2.width = 100;
  canvas2.height = 100;
  var half = canvas2.width / 2,
  gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
  gradient2.addColorStop(0.025, '#CCC');
  gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
  gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
  gradient2.addColorStop(1, 'transparent');
  
  ctx2.fillStyle = gradient2;
  ctx2.beginPath();
  ctx2.arc(half, half, half, 0, Math.PI * 2);
  ctx2.fill();
  
  // End cache
  
  function random(min:number, max=0) {
  if (arguments.length < 2) {
    max = min;
    min = 0;
  }
  
  if (min > max) {
    var hold = max;
    max = min;
    min = hold;
  }
  
  return Math.floor(Math.random() * (max - min + 1)) + min;
  }
  
  function maxOrbit(x:number, y:number) {
  var max = Math.max(x, y),
    diameter = Math.round(Math.sqrt(max * max + max * max));
  return diameter / 2;
  //星星移动范围，值越大范围越小，
  }
  interface IntStart{
  orbitRadius:number;
  radius:number;
  orbitX:number;
  orbitY:number
  timePassed:number;
  speed:number;
  alpha:number;
  draw:()=>void;
  }
  var Star = function(this: IntStart) {
  
  this.orbitRadius = random(maxOrbit(w, h));
  this.radius = random(60, this.orbitRadius) / 18; 
  //星星大小
  this.orbitX = w / 2;
  this.orbitY = h / 2;
  this.timePassed = random(0, maxStars);
  this.speed = random(this.orbitRadius) / 800000; 
  //星星移动速度
  this.alpha = random(2, 50) / 30;
  
  count++;
  stars[count] = this;
  }
  
  Star.prototype.draw = function() {
  var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
    y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
    twinkle = random(10);
  
  if (twinkle === 1 && this.alpha > 0) {
    this.alpha -= 0.05;
  } else if (twinkle === 2 && this.alpha < 1) {
    this.alpha += 0.05;
  }
  
  ctx.globalAlpha = this.alpha;
  ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
  this.timePassed += this.speed;
  }
  
  for (var i = 0; i < maxStars; i++) {
  new Star.prototype.constructor();
  }
  
  function animation() {
  ctx.globalCompositeOperation = 'source-over';
  ctx.globalAlpha = 0.9; //尾巴
  ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
  ctx.fillRect(0, 0, w, h)
  
  ctx.globalCompositeOperation = 'lighter';
  for (var i = 1, l = stars.length; i < l; i++) {
    stars[i].draw();
  };
  
  window.requestAnimationFrame(animation);
  }
  
  animation();
  }
  